1. Field of the Invention
The present invention relates to intermittent motion devices, and more particularly to fluid-operated clutch-brake devices.
2. Description of the Prior Art
Fluid operated clutch-brake devices are well known in the art. Two such devices are described in U.S. Pat. Nos. 3,378,121 and 4,381,833. However, the devices of these earlier patents make no provision for either removal, interchangeability, or field servicing of the brake and clutch units. When the annular friction ring on either the clutch side or the brake side becomes worn and in need of replacement the entire unit typically must be returned to a service center. Preloading of the rotating members is accomplished on the shaft by BELLEVILLE.TM. washers.
Tests performed on the devices of the earlier patents showed that after the brake, or clutch, is switched on there is an initial delay period of 3 to 3.5 milliseconds before any activity occurs. It was determined that the bulk of this time is attributable to energizing, de-energizing, and getting the vacuum blocking disc off the electromagnet to change the air flow.
Tests performed on the devices of the earlier patents also revealed that an undesirable overlap occurs. For a period of time both the clutch and brake are on at the same time. This results in putting an extra load on the motor and more wear on the friction ring. The emphasis in the past has typically been on energizing the electromagnets as quickly as possible with little thought given to rapid de-energization. Thus, engagement is predictably occurring quickly while disengagement takes somewhat longer which results in the overlap detected in the tests.
Tests performed on the devices of the earlier patents additionally showed that an air gap around the electromagnets and the associated vacuum blocking discs is necessary even when magnetic field reversal is utilized. The tests demonstrated that a sufficient air gap is necessary to allow atmospheric pressure to flow into the chamber before the plates release. Once the seal between the plates is broken atmospheric pressure can flow in through both openings.
Finally, tests performed on the devices of the earlier patents indicate that the practical effect of a transverse annular wall around the edge of the flexible disk may well be negligible. The tests indicate that it is the gap between the annular friction ring and the resilient disk which is the essential factor in performance. As the friction ring wears down and the gap between it and the resilient disk widens, the performance of the device drops off regardless of the presence of a transverse annular wall at the edge of the resilient disk. Thus, the key factor in extending the performance of a clutch-brake device appears to be maintaining the gap between the annular friction ring and the resilient disk within a preferred range.
Therefore, there is a need for an improved clutch-brake device which provides for serviceability in the field by allowing the convenient removal and interchangeability of individual clutch and brake units, as well as a means for easily adjusting the gap between the annular friction ring and the resilient disk when the annular friction ring becomes worn, and additionally which provides enhanced performance by alleviating the aforementioned problems associated with contemporary clutch-brake devices.